The presently disclosed embodiments are directed to a wear and cracking imaging member with extended life used in electrostatography. More particularly, the disclosure embodiments pertain to the formulation of a mechanical function improved electrophotographic imaging member by (1) creating a corona resistant charge transport layer by incorporating an ozone quenching compound and also with (2) the inclusion of a mechanically robust protective overcoat layer to add complementary enhancement effect for achieving the imaging member's wear life extension as well as providing a methodology for making and using the member.
In electrostatographic reproducing apparatuses, including digital, image on image, and contact electrostatic printing apparatuses, a light image of an original to be copied is typically recorded in the form of an electrostatic latent image upon a photosensitive member and the latent image is subsequently rendered visible by the application of electroscopic thermoplastic resin particles and pigment particles, or toner. Electrostatographic imaging members are typically in either rigid drum design or a flexible belt configuration and they are well known in the art. Typical electrostatographic imaging members include, for example: (1) electrophotographic imaging members (photoreceptors) commonly utilized in electrophotographic (xerographic) processing systems; (2) electroreceptors such as ionographic imaging members for electrographic imaging systems; and (3) intermediate transfer members such as an intermediate toner image transferring member which is used to remove the toner images from a photoreceptor surface and then transfer the very images onto a receiving paper. Although the scope of the present disclosure covers the preparation of all types of electrostatographic imaging members, however for reason of simplicity, the embodiments and discussion thus followed hereinafter will be focused and represented solely by electrophotgraphic imaging member in both rigid drum and flexible belt configurations.
Electrophotographic flexible belt imaging members may include a photoconductive layer including a single layer or composite layers. Typical electrophotographic imaging member belts include a charge transport layer and a charge generating layer on one side of a flexible supporting substrate layer and an anticurl back coating coated onto the opposite side of the substrate layer. However, a typical electrographic imaging member belt does have a more simple material structure; it includes a dielectric imaging layer on one side of a flexible supporting substrate and an anti-curl back coating on the opposite side of the substrate to render flatness.
Since both flexible electrophotographic imaging member belts and flexible electrographic imaging member belts do exhibit undesirable upward imaging member curling after completion of the electrically active coating layer(s), an anticurl back coating, applied to the backside, is required to balance the curl; the application of the anticurl back coating is therefore necessary to provide the appropriate imaging member belts with desirable flatness. The flexible electrophotographic imaging member belts and flexible electrographic imaging member belts may be seamless or seamed belts; and seamed belts are usually formed by cutting a rectangular sheet from a web, overlapping opposite ends, and welding the overlapped ends together to form a welded seam. By comparison, electrostatographic imaging members in drum design do not required an anticurl back coating, because they all have a rigid substrate drum to support the applied coating layer(s). When functioned under the electrophotographic machine service conditions, the imaging members do exhibit typical mechanical failures such as frictional abrasion, wear, and surface cracking. Surface cracking, frequently seen, is unique in belt members and is induced either due to dynamic fatigue belt flexing over the supporting rollers of a machine belt support module or caused by exposure to airborne chemical contaminants such as solvent vapors, and very particularly, the corona species emitted by machine charging subsystems, or exacerbated by the combination effects of fatigue belt flexing and airborne chemical exposure. Imaging member surface wear is found to be particularly severe in rigid drum design employing a contacting AC Bias Charging Roll to cause early onset of functional failure. Since theses pre-mature mechanical failures have prevented the imaging members to reach their intended service life and very costly to have each replacement, therefore a solution to the issue is urgently needed.
One type of composite photoconductive layer used in xerography is illustrated in U.S. Pat. No. 4,265,990 which describes a negatively-charged photosensitive member having at least two electrically operative layers. One layer comprises a photoconductive layer which is capable of photogenerating holes and injecting the photogenerated holes into a contiguous charge transport layer. Generally, where the two electrically operative layers are supported on a conductive layer, the photoconductive layer is sandwiched between a contiguous charge transport layer and the supporting conductive layer. Alternatively, the charge transport layer of a positively-charged imaging member is sandwiched between the supporting electrode and a photoconductive layer. Photosensitive members having at least two electrically operative layers, as disclosed above, provide excellent electrostatic latent images when charged in the dark with a uniform negative electrostatic charge, exposed to a light image and thereafter developed with finely divided electroscopic marking particles. The resulting toner image is usually transferred to a suitable receiving member such as paper or to an intermediate transfer member which thereafter transfers the image to a receiving member such as paper.
In the case where the charge generating layer is sandwiched between the outermost exposed charge transport layer and the electrically conducting layer, the outer surface of the charge transport layer is charged negatively and the conductive layer is charged positively. The charge generating layer then should be capable of generating electron hole pair when exposed image wise and inject only the holes through the charge transport layer. In the alternate case when the charge transport layer is sandwiched between the charge generating layer and the conductive layer, the outer surface of Gen layer is charged positively while conductive layer is charged negatively and the holes are injected through from the charge generating layer to the charge transport layer. The charge transport layer should be able to transport the holes with as little trapping of charge as possible. In a typical flexible imaging member web like photoreceptor, the charge conductive layer may be a thin coating of metal on a flexible substrate support layer.
As more advanced, higher speed electrophotographic copiers, duplicators and printers were developed, however, degradation of image quality was encountered during extended cycling. The complex, highly sophisticated duplicating and printing systems operating at very high speeds have placed stringent requirements including narrow operating limits on photoreceptors. For example, the numerous layers used in many modern photoconductive imaging members must be highly flexible, adhere well to adjacent layers, and exhibit predictable electrical characteristics within narrow operating limits to provide excellent toner images over many thousands of cycles. One type of multilayered photoreceptor that has been employed as a belt in electrophotographic imaging systems comprises a substrate, a conductive layer, an optional blocking layer, an optional adhesive layer, a charge generating layer, a charge transport layer and a conductive ground strip layer adjacent to one edge of the imaging layers, and an optional overcoat layer adjacent to another edge of the imaging layers. Such a photoreceptor usually further comprises an anticurl back coating layer on the side of the substrate opposite the side carrying the conductive layer, support layer, blocking layer, adhesive layer, charge generating layer, charge transport layer and other layers.
Conventional photoreceptors and their materials are disclosed in Katayama et al., U.S. Pat. No. 5,489,496; Yashiki, U.S. Pat. No. 4,579,801; Yashiki, U.S. Pat. No. 4,518,669; Seki et al., U.S. Pat. No. 4,775,605; Kawahara, U.S. Pat. No. 5,656,407; Markovics et al., U.S. Pat. No. 5,641,599; Monbaliu et al., U.S. Pat. No. 5,344,734; Terrell et al., U.S. Pat. No. 5,721,080; and Yoshihara, U.S. Pat. No. 5,017,449, which are herein all incorporated by reference.
More recent photoreceptors are disclosed in Fuller et al., U.S. Pat. No. 6,200,716; Maty et al., U.S. Pat. No. 6,180,309; and Dinh et al., U.S. Pat. No. 6,207,334, which are all herein incorporated by reference.
U.S. Pat. No. 6,326,111, the disclosure of which is entirely incorporated by herein by reference, relates to a charge transport material for a photoreceptor includes at least a polycarbonate polymer, at least one charge transport material, polytetrafluoroethylene (PTFE) particle aggregates having an average size of less than about 1.5 microns, hydrophobic silica and a fluorine-containing polymeric surfactant dispersed in a solvent. The presence of the hydrophobic silica enables the dispersion to have superior stability by preventing settling of the PTFE particles. A resulting charge transport layer produced from the dispersion exhibits excellent wear resistance against contact with an AC bias charging roll, excellent electrical performance, and delivers superior print quality.
U.S. Pat. No. 6,337,166, the disclosure of which is totally incorporated by reference, discloses a charge transport material for a photoreceptor includes at least a polycarbonate polymer binder having a number average molecular weight of not less than 35,000, at least one charge transport material, polytetrafluoroethylene (PTFE) particle aggregates having an average size of less than about 1.5 microns, and a fluorine-containing polymeric surfactant dispersed in a solvent mixture of at least tetrahydrofuran and toluene. The dispersion is able to form a uniform and stable material ideal for use in forming a charge transport layer of a photoreceptor. The resulting charge transport layer exhibits excellent wear resistance against contact with an AC bias charging roll, excellent electrical performance, and delivers superior print quality.
Lin et al., U.S. Pat. No. 7,413,835 issued on Aug. 19, 2008, discloses an electrophotographic imaging member having a thermoplastic charge transport layer comprising charge transport compound, a polycarbonate binder, a particular dispersion, and a high boiler compatible organic liquid. The disclosed charge transport layer exhibits enhanced wear resistance, excellent photoelectrical property, and good copy print out quality.
Yu et al., U.S. Pat. No. 7,008,741 issued on Mar. 7, 2006, discloses a photoconductive imaging member containing a photogenerating layer, a charge transport layer, or a plurality of charge transport layers, and which charge transport layer, especially the top charge transport layer contains a vinyl organic compound.
Conventional photoreceptors and their materials are disclosed in Katayama et al., U.S. Pat. No. 5,489,496; Yashiki, U.S. Pat. No. 4,579,801; Yashiki, U.S. Pat. No. 4,518,669; Seki et al., U.S. Pat. No. 4,775,605; Kawahara, U.S. Pat. No. 5,656,407; Markovics et al., U.S. Pat. No. 5,641,599; Monbaliu et al., U.S. Pat. No. 5,344,734; Terrell et al., U.S. Pat. No. 5,721,080; and Yoshihara, U.S. Pat. No. 5,017,449, which are herein all incorporated by reference.
More recent photoreceptors are disclosed in Fuller et al., U.S. Pat. No. 6,200,716; Maty et al., U.S. Pat. No. 6,180,309; and Dinh et al., U.S. Pat. No. 6,207,334, which are all herein incorporated by reference.
Since the outermost exposed charge transport layer of both flexible belt and rigid drum electrophotographic imaging members do exhibit pre-mature onset of abrasion/wear mechanical failure caused by corona attack, the formulation of a robust and functional charge transport layer is needed to resolve the issue. To further enhance the service life of the imaging member, a wear resistant overcoat layer may be added over the charge transport layer to provide abrasion and wear protection for further extension of the service life of the imaging members in the field.
The terms used to describe the imaging members, their layers and respective compositions, may each be used interchangeably with alternative phrases known to those of skill in the art. The terms used herein are intended to cover all such alternative phrases.